Zoom lens

ABSTRACT

A zoom lens includes sequentially from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power. The zoom lens satisfies given conditions to implement a compact, large aperture ratio zoom lens having excellent optical performance and compatible with solid state image sensors capable of recording full high vision images.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens suitable for an imagingapparatus equipped with a solid state image sensor, such as digitalstill camera and a digital video camera.

2. Description of the Related Art

Zoom lenses that are configured by 4 lens groups, capable of high zoomratios, and used as imaging lens on digital still cameras and digitalvideo cameras equipped with a solid state image sensor such as such as acharge-coupled device (CCD) and a complementarymetal-oxide-semiconductor (CMOS) are commonly known (see, for example,Japanese Patent No. 4672860).

The zoom lens recited in Japanese Patent No. 4672860 includessequentially from a side nearest an object (object side), first tofourth lens groups respectively having a positive, negative, positive,and positive refractive powers. In the zoom lens, the first and thirdlens groups are stationary, while the second lens group is moved in onedirection to perform zooming and the fourth lens group is moved in aback and forth direction to correct image plane variation accompanyingzooming and to perform focusing. The zoom ratio of the zoom lens is onthe order of 25×; and the maximum angle of view is on the order of 58degrees. With such a zoom lens formed by 4 lens groups, since there are2 movable groups, configuration of the lens barrel can be simplified andthe size of the lens system overall can be reduced.

A zoom lens that incorporates a stationary fifth lens group into the 4lens group configuration above is further known (see, for example,Japanese Patent Nos. 4542933, 4823680, and 4823684). The zoom lensesrecited in Japanese Patent Nos. 4542933, 4823680, and 4823684 eachinclude from the object side, first to fifth lens groups respectivelyhaving a positive, negative, positive, positive, and negative refractivepower. In the zoom lenses, the first, third, and fifth lens groups arestationary, while the second lens group is moved in one direction toperform zooming and the fourth lens group is moved in a back and forthdirection to correct image plane variation accompanying zooming and toperform focusing.

The zoom ratio of the zoom lens recited in Japanese Patent No. 4542933is on the order of 30×; and the maximum angle of view is on the order of60 degrees. The zoom ratio of the zoom lens recited in Japanese PatentNo. 4823680 is on the order of 35×; and the maximum angle of view is onthe order of 73 degrees. The zoom ratio of the zoom leas recited inJapanese Patent No. 4823604 is on the order of 14×; and the maximumangle of view is on the order of 70 degrees.

Nonetheless, in addition to favorably correcting various types ofaberration over the entire zoom range, large aperture ratios for wideangle views enabling the recording of images at dimly lit locations overa wider range are demanded of lens systems for surveillance cameras.Furthermore, accompanying the increased prevalence of solid state imagesensors capable of full high vision image recording, lens systemscompatible with full high vision solid state image sensors are demanded.Conventionally, demand has increased for a lens system for asurveillance camera equipped with a full high vision solid state imagesensor to have extremely high optical performance capable of favorablycorrecting various types of aberration over the entire zoom range.

As conventional technologies, the zoom lenses above have a problem inthat accompanying increased aperture ratios and higher zoom ratios, atthe telephoto edge where the zoom ratio is high, image plane curvaturebecomes prominent when the object distance changes. As a result,particularly at the telephoto edge, as the object distance becomescloser, a peripheral portion of the image gradually becomes out offocus. Of course, the greater the image height, i.e., the larger thesize of the solid state image sensor, the more prominent the blurbecomes.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least solve the aboveproblems in the conventional technologies.

A zoom lens according to one aspect of the present invention includessequentially from an object side, a first lens group having a positiverefractive power, a second lens group having a negative refractivepower, a third lens group having a positive refractive power, a fourthlens group having a positive refractive power, and a fifth lens grouphaving a negative refractive power. The first lens group, the third lensgroup, and the fifth lens group remain stationary. The second lens groupis moved along an optical axis, from the object side toward an imageside, whereby zooming from a wide angle edge to a telephoto edge isperformed. The fourth lens group is moved along the optical axis,whereby image plane variation accompanying zooming is corrected andfocusing is performed. The fifth lens group includes sequentially fromthe object side, a negative first lens having at least one asphericsurface and a positive second lens. The zoom lens satisfies aconditional expression (1) 1.5<|f51|/Y<3, and a conditional expression(2) 0.2<|F5/Ft|<0.8, where, f51 is a focal length of the first lens inthe fifth lens group, Y is an image height for the entire opticalsystem, F5 is a focal length of the fifth lens group, and Ft is a focallength of the entire optical system at the telephoto edge.

The other objects, features, and advantages of the present invention arespecifically set forth in or will become apparent from the followingdetailed description of the invention when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view (along the optical axis) of a zoom lensaccording to a first embodiment;

FIG. 2 is a diagram of various types of aberration occurring, withrespect to the d-line (λ=587.56 nm), in the zoom lens according to thefirst embodiment;

FIG. 3 is a cross sectional view (along the optical axis) of the zoomlens according to a second embodiment;

FIG. 4 is a diagram of various types of aberration occurring, withrespect to the d-line (λ=587.56 nm), in the zoom lens according to thesecond embodiment;

FIG. 5 is a cross sectional view (along the optical axis) of the zoomlens according to a third embodiment;

FIG. 6 is a diagram of various types of aberration occurring, withrespect to the d-line (λ=587.56 nm), in the zoom lens according to thethird embodiment;

FIG. 7 is a cross sectional view (along the optical axis) of the zoomlens according to a fourth embodiment; and

FIG. 8 is a diagram of various types of aberration occurring, withrespect to the d-line (λ=587.56 nm), in the zoom lens according to thefourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of a zoom lens according to the present inventionare explained in detail with reference to the accompanying drawings.

The zoom lens according to the present invention includes sequentiallyfrom the object side, a first lens group having a positive refractivepower, a second lens group having a negative refractive power, a thirdlens group having a positive refractive power, a fourth lens grouphaving a positive refractive power, and a fifth lens group having anegative refractive power. The second lens group is moved along anoptical axis, whereby zooming is performed from the wide angle edge tothe telephoto edge. The fourth lens group is moved along the opticalaxis whereby image plane variation accompanying zooming is corrected andfocusing is performed. The first lens group, the third lens group, andthe fifth lens group remain stationary (the configuration above isreferred to as a basic configuration).

An object of the present invention is to provide a high zoom ratio zoomlens that is compact, has a large aperture ratio and excellent opticalperformance, e.g., a zoom lens that is optimal for a compact imagingapparatus equipped with a solid state image sensor capable of recordingimages in full high vision. To achieve such an object, variousconditions are set as indicated below.

In addition to the basic configuration, in the zoom lens according tothe present invention, the fifth lens group includes sequentially fromthe object side, a negative first lens having at least one asphericsurface and a positive second lens. By forming an aspheric surface onthe first lens disposed farthest on the object side of the fifth lensgroup, coma, astigmatism, and image plane curvature that accompany highzoom ratios and large aperture ratios and occur when the object distancechanges, can be easily corrected. As a result, the advantages of highzoom ratios and large aperture ratios can be realized.

The zoom lens according to the present invention preferably satisfiesthe following conditional expressions, where f51 is the focal length ofthe first lens in the fifth lens group, Y is the image height for theentire optical system, F5 is the focal length of the fifth lens group,and Ft is the focal length of the entire optical system at the telephotoedge.1.5<|f51|/Y<3  (1)0.2<|F5/Ft|<0.8  (2)

Conditional expression (1) prescribes a proper range of the ratio of thefocal length f51 of the first lens disposed farthest on the object sideof the fifth lens group and the image height Y of the entire opticalsystem. Satisfaction of conditional expression (1) establishes a properrefractive power of the negative first lens disposed farthest on theobject side of the fifth lens group, enabling implementation of ahigh-resolution optical system of a high zoom ratio and favorablycorrecting various types of aberration.

Below the lower limit of conditional expression (1), the negativerefractive power of the first lens disposed farthest on the object sideof the fifth lens group becomes too strong, making correction of variousaberration of a peripheral portion of an image difficult. Meanwhile,above the upper limit of conditional expression (1), the negativerefractive power of the first lens disposed farthest on the object sideof the fifth lens group becomes too weak, increasing the Petzval sum forthe entire fifth lens group and making image plane curvature prominent,whereby a flat imaging plane cannot be obtained. In particular, thecorrection of chromatic aberration occurring on the telephoto sidebecomes difficult.

More favorable results can be expected if the zoom lens satisfiesconditional expression (1) within the range indicated below.1.7<|f51|/Y<2.8  (1a)By satisfying conditional expression (1) within the range prescribed byconditional expression (1a), the zoom lens can more favorably correctvarious types of aberration of the peripheral portion of an image sincethe Petzval sum for the entire fifth lens group can be decreased.

Conditional expression (2) prescribes a proper range of the ratio of thefocal length F5 of the fifth lens group and the focal length Ft of theentire optical system at the telephoto edge. Below the lower limit ofconditional expression (2), the refractive power of the fifth lens groupbecomes too strong, the exit pupil position on the telephoto sidebecomes extremely close to the image plane, and relative illumination(shading) deteriorates. Further, spherical aberration and coma on thewide angle side or the telephoto side becomes prominent, inviting dropsin resolution. Meanwhile, above the upper limit of conditionalexpression (2), the refractive power of the fifth lens group becomes tooweak, requiring the fourth lens group to be moved over a greaterdistance to perform focusing and thereby, making size reductions of theoptical system difficult.

To achieve high resolution, the zoom lens according to the presentinvention preferably satisfies the following conditional expression,where nd51 is the refractive index (with respect to the d-line) of thefirst lens in the fifth lens group and nd52 is refractive index (withrespect to the d-line) of the second lens in the fifth lens group.nd51−nd52>0.2  (3)

Conditional expression (3) prescribes a proper range of the differenceof the refractive indexes (with respect to the d-line) of the negativelens (the first lens) and the positive lens (the second lens) in thefifth lens group. Below the lower limit of conditional expression (3),the Petzval sum for the entire fifth lens group increases and imageplane curvature becomes prominent, whereby a flat imaging plane cannotbe obtained. As a result, resolution of the optical system drops.

In the zoom lens according to the present invention, the first lensgroup includes sequentially from the object side, a negative first lens,a positive second lens, a positive third lens, and a positive fourthlens. In the configuration, to favorably correct chromatic aberration atthe telephoto edge of the optical system, the first lens and second lensin the first lens group are cemented. In addition, the zoom lenspreferably satisfies the following conditional expression, where υd12 isthe Abbe number (with respect to the d-line) of the second lens in thefirst lens group, and υd13 is the Abbe number (with respect to thed-line) of the third lens in the first lens group.υd12>75  (4)υd13>63  (5)

Conditional expressions (4) and (5) express conditions necessary tofavorably correct chromatic aberration occurring at the telephoto edgeof the optical system. Below the lower limit of either conditionalexpression (4) or conditional expression (5), chromatic aberrationoccurring at the telephoto edge of the optical system cannot becorrected.

In the zoom lens according to the present invention, the third lensgroup preferably includes sequentially from the object side, a positivefirst lens having at least one aspheric surface, and a negative secondlens that is a meniscus lens having a convex surface on the object side.Configuration of the third lens group in this manner enables sphericalaberration and coma occurring over the entire zoom range to be favorablycorrected.

As described, the zoom lens according to the present invention has theconfiguration described above, enabling size reductions, a greateraperture ratio, and a higher zoom ratio to be achieved as well asfavorable correction of various types of aberration over the entire zoomrange and compatibility with a solid state image sensor capable ofrecording full high vision images. In particular, by satisfying theconditions above, the zoom lens enables size reductions, greateraperture ratios, higher zoom ratios, and the maintenance of high opticalperformance to be achieved.

With reference to the accompanying drawings, embodiments of the zoomlens according to the present invention will be described in detail.Nonetheless, the present invention is not limited by the embodimentsbelow.

FIG. 1 is a cross sectional view (along the optical axis) of the zoomlens according to a first embodiment. The zoom lens includessequentially from a side nearest a non-depicted object (the objectside), a first lens group G₁₁ having a positive refractive power, asecond lens group G₁₂ having a negative refractive power, a third lensgroup G₁₃ having a positive refractive power, a fourth lens group G₁₄having a positive refractive power, and a fifth lens group G₁₅ having anegative refractive power.

An aperture stop STP prescribing a given aperture is disposed betweenthe second lens group G₁₂ and the third lens group G₁₃. A cover glass CGis disposed between the fifth lens group G₁₅ and an imaging plane IMG.The cover glass CG is disposed as necessary and may be omittedaccordingly. At the image plane IMG, the light receiving surface of asolid state image sensor, such as a CCD and CMOS, is disposed.

The first lens group G₁₁ includes sequentially from the object side, anegative first lens L₁₁₁, a positive second lens L₁₁₂, a positive thirdlens L₁₁₃, and a positive fourth lens L₁₁₄. The first lens L₁₁₁ and thesecond lens L₁₁₂ are cemented.

The second lens group G₁₂ includes sequentially from the object side, anegative first lens L₁₂₁, a negative second lens L₁₂₂, a positive thirdlens L₁₂₃, and a negative fourth lens L₁₂₄. The first lens L₁₂₁ is ameniscus lens having a convex surface on the object side and bothsurfaces of the first lens L₁₂₁ are aspheric. The third lens L₁₂₃ andthe fourth lens L₁₂₄ are cemented.

The third lens group G₁₃ includes sequentially from the object side, apositive first lens L₁₃₁ and a negative second lens L₁₃₂. Both surfacesof the first lens L₁₃₁ are aspheric. The second lens L₁₃₂ is a meniscuslens having a convex surface on the object side.

The fourth lens group G₁₄ includes sequentially from the object side, apositive first lens L₁₄₁ and a negative second lens L₁₄₂. The surface onthe object side of the first lens L₁₁₁ aspheric. The first lens L₁₄₁ andthe second lens L₁₄₂ are cemented.

The fifth lens group G₁₅ includes sequentially from the object side, anegative first lens L₁₅₁ and a positive second lens L₁₅₂. Both surfacesof the first lens L₁₅₁ are aspheric.

The second lens group G₁₂ is moved along the optical axis from theobject side toward the imaging plane IMG side, whereby the zoom lenszooms from the wide angle edge to the telephoto edge. The fourth lensgroup G₁₄ is moved along the optical axis, whereby the zoom lenscorrects image plane variations accompanying zooming and performsfocusing. The first lens group G₁₁, the third lens group G₁₃, and thefifth lens group G₁₅ remain stationary.

Here, various values related to the zoom lens according to the firstembodiment are given.

Focal length of entire lens system = 4.3 (wide angle edge) to 24.0(intermediate focal position) to 129.0 (Ft: telephoto edge) F number =1.6 (wide angle edge) to 3.8 (intermediate focal position) to 4.9(telephoto edge) Half-angle (ω) = 38.03 (wide angle edge) to 7.10(intermediate focal position) to 1.32 (telephoto edge) (Lens Data) r₁ =155.252 d₁ = 1.00 nd₁ = 1.84666 νd₁ = 23.78 r₂ = 40.511 d₂ = 5.75 nd₂ =1.49700 νd₂ = 81.60 r₃ = −245.543 d₃ = 0.10 r₄ = 55.154 d₄ = 3.20 nd₃ =1.59282 νd₃ = 68.63 r₅ = 382.377 d₅ = 0.10 r₆ = 31.841 d₆ = 3.50 nd₄ =1.83481 νd₄ = 42.72 r₇ = 95.333 d₇ = D(7) (variable) r₈ = 73.450(aspheric) d₈ = 0.70 nd₅ = 1.85135 νd₅ = 40.10 r₉ = 6.869 (aspheric) d₉= 3.52 r₁₀ = −11.337 d₁₀ = 0.50 nd₆ = 1.88300 νd₆ = 40.80 r₁₁ = 339.750d₁₁ = 0.10 r₁₂ = 23.770 d₁₂ = 2.00 nd₇ = 1.95906 νd₇ = 17.47 r₁₃ =−24.162 d₁₃ = 0.50 nd₈ = 1.88300 νd₈ = 40.80 r₁₄ = 104.181 d₁₄ = D(14)(variable) r₁₅ = ∞ (aperture stop) d₁₅ = 0.50 r₁₆ = 11.539 (aspheric)d₁₆ = 4.20 nd₉ = 1.61881 νd₉ = 63.85 r₁₇ = −30.000 (aspheric) d₁₇ = 0.10r₁₈ = 19.101 d₁₈ = 0.80 nd₁₀ = 2.001 νd₁₀ = 29.13 r₁₉ = 10.836 d₁₉ =D(19) (variable) r₂₀ = 12.791 (aspheric) d₂₀ = 4.20 nd₁₁ = 1.4971 νd₁₁ =81.56 r₂₁ = −9.500 d₂₁ = 0.60 nd₁₂ = 1.90366 νd₁₂ = 31.31 r₂₂ = −14.070d₂₂ = D(22) (variable) r₂₃ = 28.595 (aspheric) d₂₃ = 0.50 nd₁₃ = 1.85135νd₁₃ = 40.10 r₂₄ = 5.300 (aspheric) d₂₄ = 0.30 r₂₅ = 7.909 d₂₅ = 2.26nd₁₄ = 1.56732 νd₁₄ = 42.80 r₂₆ = −16.411 d₂₆ = 1.00 r₂₇ = ∞ d₂₇ = 2.00nd₁₅ = 1.51633 νd₁₅ = 64.14 r₂₈ = ∞ d₂₈ = 3.50 r₂₉ = ∞ (imaging plane)Constants of the cone (k) and aspheric coefficients (A, B, C, D) (eighthplane) k = 0, A = −4.57687 × 10⁻⁵, B = 6.79061 × 10⁻⁶, C = −2.31578 ×10⁻⁷, D = 2.42224 × 10⁻⁹ (ninth plane) k = 0.5967, A = −3.17031 × 10⁻⁴,B = −4.17155 × 10⁻⁶, C = 5.67706 × 10⁻⁷, D = −3.92278 × 10⁻⁸ (sixteenthplane) k = −0.1306, A = −4.08183 × 10⁻⁵, B = −1.15089 × 10⁻⁶, C =1.15662 × 10⁻⁸, D = −6.70182 × 10⁻¹¹ (seventeenth plane) k = −8.2910, A= 7.81968 × 10⁻⁵, B = −1.89538 × 10⁻⁶, C = 2.76889 × 10⁻⁸, D = −1.55839× 10⁻¹⁰ (twentieth plane) k = −0.1487, A = −4.90625 × 10⁻⁵, B = −1.02186× 10⁻⁶, C = 5.04342 × 10⁻¹⁰, D = 4.85594 × 10⁻¹⁰ (twenty-third plane) k= 0, A = −4.98290 × 10⁻⁴, B = −1.45444 × 10⁻⁵, C = 3.32964 × 10⁻⁶, D =−1.57350 × 10⁻⁷ (twenty-fourth plane) k = −0.1993, A = −4.77089 × 10⁻⁴,B = −3.50309 × 10⁻⁵, C = 3.89261 × 10⁻⁶, D = −2.07190 × 10⁻⁷ (Zoom Data)wide angle intermediate telephoto edge focal position edge D(7) 0.71919.460 27.823 D(14) 28.930 10.189 1.825 D(19) 10.283 4.604 14.356 D(22)4.687 10.366 0.614 (Values related to conditional expression (1)) f51(focal length of first lens L₁₅₁) = −7.718 Y (image height) = 3.4|f51|/Y = 2.27 (Values related to conditional expression (2)) F5 (focallength of fifth lens group G₁₅) = −58.051 |F5/Ft| = 0.45 (Values relatedto conditional expression (3)) nd51 (refractive index of first lensL₁₅₁, with respect to d-line) = 1.85135 nd52 (refractive index of secondlens L₁₅₂, with respect to d-line) = 1.56732 nd51 − nd52 = 0.284 (Valuesrelated to conditional expression (4)) νd12 (Abbe number of second lensL₁₁₂, with respect to d-line) = 81.60 (Values related to conditionalexpression (5)) νd13 (Abbe number of third lens L₁₁₃, with respect tod-line) = 68.63

FIG. 2 is a diagram of various types of aberration occurring, withrespect to the d-line (λ=587.56 nm), in the zoom lens according to thefirst embodiment. S and M shown with respect to astigmatism,respectively indicate aberration at the sagittal image plane and at themeridonal image plane.

FIG. 3 is a cross sectional view (along the optical axis) of the zoomlens according to a second embodiment. The zoom lens includessequentially from the object side, a first lens group G₂₁ having apositive refractive power, a second lens group G₂₂ having a negativerefractive power, a third lens group G₂₃ having a positive refractivepower, a fourth lens group G₂₄ having a positive refractive power, and afifth lens group G₂₅ having a negative refractive power.

The aperture stop STP prescribing a given aperture is disposed betweenthe second lens group G₂₂ and the third lens group G₂₃. The cover glassCG is disposed between the fifth lens group G₂₅ and the imaging planeIMG. The cover glass CG is disposed as necessary and may be omittedaccordingly. At the image plane IMG, the light receiving surface of asolid state image sensor, such as a CCD and CMOS, is disposed.

The first lens group G₂₁ includes sequentially from the object side, anegative first lens L₂₁₁, a positive second lens L₂₁₂, a positive thirdlens L₂₁₃, and a positive fourth lens L₂₁₄. The first lens L₂₁₁ and thesecond lens L₂₁₂ are cemented.

The second lens group G₂₂ includes sequentially from the object side, anegative first lens L₂₂₁, a negative second lens L₂₂₂, a positive thirdlens L₂₂₃, and a negative fourth lens L₂₂₄. The first lens L₂₂₁ is ameniscus lens having a convex surface on the object side and bothsurfaces of the first lens L₂₂₁ are aspheric. The third lens L₂₂₃ andthe fourth lens L₂₂₄ are cemented.

The third lens group G₂₃ includes sequentially from the object side, apositive first lens L₂₃₁ and a negative second lens L₂₃₂. Both surfacesof the first lens L₂₃₁ are aspheric. The second lens L₂₃₂ is a meniscuslens having a convex surface on the object side.

The fourth lens group G₂₄ includes sequentially from the object side, apositive first lens L₂₄₁ and a negative second lens L₂₄₂. The surface onthe object side of the first lens L₂₄₁ is aspheric. The first lens L₂₄₁and the second lens L₂₄₂ are cemented.

The fifth lens group G₂₅ includes sequentially from the object side, anegative first lens L₂₅₁ and a positive second lens L₂₅₂. Both surfacesof the first lens L₂₅₁ are aspheric.

The second lens group G₂₂ is moved along the optical axis from theobject side toward the imaging plane IMG side, whereby the zoom lenszooms from the wide angle edge to the telephoto edge. The fourth lensgroup G₂₄ is moved along the optical axis, whereby the zoom lenscorrects image plane variations accompanying zooming and performsfocusing. The first group G₂₁ the third lens group G₂₃, and the fifthlens group G₂₅ remain stationary.

Here, various values related to the zoom lens according to secondembodiment are given.

Focal length of entire lens system = 4.3 (wide angle edge) to 24.0(intermediate focal position) to 129.0 (Ft: telephoto edge) F number =1.6 (wide angle edge) to 3.8 (intermediate focal position) to 4.9(telephoto edge) Half-angle (ω) = 38.09 (wide angle edge) to 7.07(intermediate focal position) to 1.32 (telephoto edge) (Lens Data) r₁ =261.122 d₁ = 1.00 nd₁ = 1.84666 νd₁ = 23.78 r₂ = 41.992 d₂ = 6.00 nd₂ =1.43700 νd₂ = 95.10 r₃ = −142.792 d₃ = 0.10 r₄ = 57.592 d₄ = 3.34 nd₃ =1.61800 νd₃ = 63.39 r₅ = 1461.086 d₅ = 0.10 r₆ = 31.613 d₆ = 3.50 nd₄ =1.88300 νd₄ = 40.80 r₇ = 91.274 d₇ = D(7) (variable) r₈ = 17.271(aspheric) d₈ = 0.70 nd₅ = 1.85135 νd₅ = 40.10 r₉ = 5.629 (aspheric) d₉= 3.82 r₁₀ = −11.166 d₁₀ = 0.50 nd₆ = 1.88300 νd₆ = 40.80 r₁₁ = 67.816d₁₁ = 0.10 r₁₂ = 19.434 d₁₂ = 2.06 nd₇ = 1.95906 νd₇ = 17.47 r₁₃ =−27.282 d₁₃ = 0.50 nd₈ = 1.88300 νd₈ = 40.80 r₁₄ = 63.676 d₁₄ = D(14)(variable) r₁₅ = ∞ (aperture stop) d₁₅ = 0.50 r₁₆ = 11.267 (aspheric)d₁₆ = 4.40 nd₉ = 1.61881 νd₉ = 63.85 r₁₇ = −25.469 (aspheric) d₁₇ = 0.10r₁₈ = 21.986 d₁₈ = 0.60 nd₁₀ = 2.001 νd₁₀ = 29.13 r₁₉ = 11.300 d₁₉ =D(19) (variable) r₂₀ = 13.021 (aspheric) d₂₀ = 4.18 nd₁₁ = 1.4971 νd₁₁ =81.56 r₂₁ = −10.019 d₂₁ = 0.60 nd₁₂ = 1.90366 νd₁₂ = 31.31 r₂₂ = −13.773d₂₂ = D(22) (variable) r₂₃ = 24.019 (aspheric) d₂₃ = 0.50 nd₁₃ = 1.85135νd₁₃ = 40.10 r₂₄ = 5.699 (aspheric) d₂₄ = 0.54 r₂₅ = 16.318 d₂₅ = 2.11nd₁₄ = 1.51633 νd₁₄ = 64.14 r₂₆ = −10.039 d₂₆ = 1.00 r₂₇ = ∞ d₂₇ = 2.00nd₁₅ = 1.51633 νd₁₅ = 64.14 r₂₈ = ∞ d₂₈ = 3.50 r₂₉ = ∞ (imaging plane)Constants of the cone (k) and aspheric coefficients (A, B, C, D) (eighthplane) k = 0, A = −6.21082 × 10⁻⁴, B = 1.34413 × 10⁻⁵, C = −1.99187 ×10⁻⁷, D = 1.35410 × 10⁻⁹ (ninth plane) k = −0.0060, A = −7.63715 × 10⁻⁴,B = −1.36437 × 10⁻⁵, C = 7. 63607 × 10⁻⁷, D = −2.94908 × 10⁻⁸ (sixteenthplane) k = −0.2311, A = −6.05478 × 10⁻⁵, B = −1.25340 × 10⁻⁶, C =1.67144 × 10⁻⁸, D = −8.95523 × 10⁻¹¹ (seventeenth plane) k = −4.7687, A= 6.98644 × 10⁻⁵, B = −1.72352 × 10⁻⁶, C = 2. 91064 × 10⁻⁸, D = −1.70266× 10⁻¹⁰ (twentieth plane) k = −0.4887, A = −7.75303 × 10⁻⁵, B = −4.64307× 10⁻⁷, C = −4.68979 × 10⁻¹¹, D = 2.32383 × 10⁻¹⁰ (twenty-third plane) k= 0, A = −6.68416 × 10⁻⁴, B = −3.85322 × 10⁻⁵, C = 7.43212 × 10⁻⁷, D =6.05435 × 10⁻⁸ (twenty-fourth plane) k = −0.2788, A = −4.36169 × 10⁻⁴, B= −7.39966 × 10⁻⁵, C = 1.04310 × 10⁻⁶, D = 8.94196 × 10⁻⁸ (Zoom Data)wide angle intermediate telephoto edge focal position edge D(7) 0.60019.459 27.778 D(14) 29.021 10.161 1.843 D(19) 9.668 4.480 13.573 D(22)4.508 9.697 0.604 (Values related to conditional expression (1)) f51(focal length of first lens L₂₅₁) = −8.889 Y (image height) = 3.4|f51|/Y = 2.614 (Values related to conditional expression (2)) F5 (focallength of fifth lens group G₂₅) = −51.206 |F5/Ft| = 0.397 (Valuesrelated to conditional expression (3)) nd51 (refractive index of firstlens L₂₅₁, with respect to d-line) = 1.85135 nd52 (refractive index ofsecond lens L₂₅₂, with respect to d-line) = 1.51633 nd51 − nd52 = 0.335(Values related to conditional expression (4)) νd12 (Abbe number ofsecond lens L₂₁₂, with respect to d-line) = 95.10 (Values related toconditional expression (5)) νd13 (Abbe number of third lens L₂₁₃, withrespect to d-line) = 63.39

FIG. 4 is a diagram of various types of aberration occurring, withrespect to the d-line (λ=587.56 nm), in the zoom lens according to thesecond embodiment. S and M shown with respect to astigmatism,respectively indicate aberration at the sagittal image plane and at themeridonal image plane.

FIG. 5 is a cross sectional view (along the optical axis) of the zoomlens according to a third embodiment. The zoom lens includessequentially from the object side, a first lens group G₃₁ having apositive refractive power, a second lens group G₃₂ having a negativerefractive power, a third lens group G₃₃ having a positive refractivepower, a fourth lens group G₃₄ having a positive refractive power, and afifth lens group G₃₅ having a negative refractive power.

The aperture stop STP prescribing a given aperture is disposed betweenthe second lens group G₃₂ and the third lens group G₃₃. The cover glassCG is disposed between the fifth lens group G₃₅ and the imaging planeIMG. The cover glass CG is disposed as necessary and may be omittedaccordingly. At the image plane IMG, the light receiving surface of asolid state image sensor, such as a CCD and CMOS, is disposed.

The first lens group G₃₁ includes sequentially from the object side, anegative first lens L₃₁₁, a positive second lens L₃₁₂, a positive thirdlens L₃₁₃, and a positive fourth lens L₃₁₄. The first lens L₃₁₁ and thesecond lens L₃₁₂ are cemented.

The second lens group G₃₂ includes sequentially from the object side, anegative first lens L₃₂₁, a negative second lens L₃₂₂, a positive thirdlens L₃₂₃, and a negative fourth lens L₃₂₄. The first lens L₃₂₁ is ameniscus lens having a convex surface on the object side and bothsurfaces of the first lens L₃₂₁ are aspheric. The third lens L₃₂₃ andthe fourth lens L₃₂₄ are cemented.

The third lens group G₃₃ includes sequentially from the object side, apositive first lens L₃₃₁ and a negative second lens L₃₃₂. Both surfacesof the first lens L₃₃₁ as aspheric. The second lens L₃₃₂ is a meniscuslens having a convex surface on the object side.

The fourth lens group G₃₄ includes sequentially from the object side, apositive first lens L₃₄₁ and a negative second lens L₃₄₂. The surface onthe object side of the first lens L₃₄₁ is aspheric. The first lens L₃₄₁and the second lens L₃₄₂ are cemented.

The fifth lens group G₃₅, includes sequentially from the object side, anegative first lens L₃₅₁ and a positive second lens L₃₅₂. Both surfacesof the first lens L₃₅₁ are aspheric.

The second lens group G₃₂ is moved along the optical axis from theobject side toward the imaging plane IMG side, whereby the zoom lenszooms from the wide angle edge to the telephoto edge. The fourth lensgroup G₃₄ is moved along the optical axis, whereby the zoom lenscorrects image plane variations accompanying zooming and performsfocusing. The first lens group G₃₁, the third lens group G₃₃, and thefifth lens group G₃₅ remain stationary.

Here, various values related to the zoom lens according to the thirdembodiment are given.

Focal length of entire lens system = 4.3 (wide angle edge) to 24.0(intermediate focal position) to 129.0 (Ft: telephoto edge) F number =1.6 (wide angle edge) to 3.8 (intermediate focal position) to 4.9(telephoto edge) Half-angle (ω) = 37.93 (wide angle edge) to 7.09(intermediate focal position) to 1.32 (telephoto edge) (Lens Data) r₁ =143.132 d₁ = 1.00 nd₁ = 1.84666 νd₁ = 23.78 r₂ = 40.225 d₂ = 5.80 nd₂ =1.43700 νd₂ = 95.10 r₃ = −220.562 d₃ = 0.10 r₄ = 57.824 d₄ = 3.28 nd₃ =1.59282 νd₃ = 68.63 r₅ = 575.311 d₅ = 0.10 r₆ = 32.258 d₆ = 3.68 nd₄ =1.83481 νd₄ = 42.72 r₇ = 106.337 d₇ = D(7) (variable) r₈ = 53.938(aspheric) d₈ = 0.70 nd₅ = 1.85135 νd₅ = 40.10 r₉ = 6.852 (aspheric) d₉= 3.63 r₁₀ = −10.409 d₁₀ = 0.50 nd₆ = 1.88300 νd₆ = 40.80 r₁₁ = −119.311d₁₁ = 0.10 r₁₂ = 32.375 d₁₂ = 1.99 nd₇ = 1.95906 νd₇ = 17.47 r₁₃ =−18.558 d₁₃ = 0.50 nd₈ = 1.88300 νd₈ = 40.80 r₁₄ = 246.052 d₁₄ = D(14)(variable) r₁₅ = ∞ (aperture stop) d₁₅ = 0.50 r₁₆ = 11.250 (aspheric)d₁₆ = 4.50 nd₉ = 1.61881 νd₉ = 63.85 r₁₇ = −25.151 (aspheric) d₁₇ = 0.14r₁₈ = 25.680 d₁₈ = 0.70 nd₁₀ = 2.001 νd₁₀ = 29.13 r₁₉ = 12.179 d₁₉ =D(19) (variable) r₂₀ = 12.463 (aspheric) d₂₀ = 4.21 nd₁₁ = 1.4971 νd₁₁ =81.56 r₂₁ = −10.285 d₂₁ = 0.60 nd₁₂ = 1.90366 νd₁₂ = 31.31 r₂₂ = −14.345d₂₂ = D(22) (variable) r₂₃ = 34.622 (aspheric) d₂₃ = 0.50 nd₁₃ = 1.85135νd₁₃ = 40.10 r₂₄ = 4.280 (aspheric) d₂₄ = 0.11 r₂₅ = 5.105 d₂₅ = 2.54nd₁₄ = 1.54814 νd₁₄ = 45.82 r₂₆ = −18.427 d₂₆ = 1.00 r₂₇ = ∞ d₂₇ = 2.00nd₁₅ = 1.51633 νd₁₅ = 64.14 r₂₈ = ∞ d₂₈ = 3.50 r₂₉ = ∞ (imaging plane)Constants of the cone (k) and aspheric coefficients (A, B, C, D) (eighthplane) k = 0, A = −1.10104 × 10⁻⁴, B = 6.86574 × 10⁻⁶, C = −1.80314 ×10⁻⁷, D = 1.77529 × 10⁻⁹ (ninth plane) k = 0.5559, A = −3.93632 × 10⁻⁴,B = −6.30197 × 10⁻⁶, C = 4.84720 × 10⁻⁷, D = −2.99161 × 10⁻⁸ (sixteenthplane) k = −0.1935, A = −5.34967 × 10⁻⁵, B = −1.15951 × 10⁻⁶, C =1.21900 × 10⁻⁸, D = −9.39982 × 10⁻¹¹ (seventeenth plane) k = −6.7682, A= 7.38246 × 10⁻⁵, B = −1.90295 × 10⁻⁶, C = 2.73786 × 10⁻⁸, D = −1.67159× 10⁻¹⁰ (twentieth plane) k = −0.4009, A = −6.89337 × 10⁻⁵, B = −1.52572× 10⁻⁶, C = 1.76743 × 10⁻⁸, D = 1.60421 × 10⁻¹⁰ (twenty-third plane) k =0, A = −4.81453 × 10⁻⁴, B = −1.75639 × 10⁻⁵, C = 1.83475 × 10⁻⁶, D =−9.28491 × 10⁻⁸ (twenty-fourth plane) k = −0.2457, A = −4.55109 × 10⁻⁴,B = −5.44365 × 10⁻⁵, C = 3.09526 × 10⁻⁶, D = −2.17589 × 10⁻⁷ (Zoom Data)wide angle intermediate telephoto edge focal position edge D(7) 0.60019.976 28.485 D(14) 29.696 10.320 1.811 D(19) 9.466 4.418 12.865 D(22)4.116 9.164 0.717 (Values related to conditional expression (1)) f51(focal length of first lens L₃₅₁) = −5.780 Y (image height) = 3.4|f51|/Y = 1.7 (Values related to conditional expression (2)) F5 (focallength of fifth lens group G₃₅) = −32.279 |F5/Ft| = 0.25 (Values relatedto conditional expression (3)) nd51 (refractive index of first lensL₃₅₁, with respect to d-line) = 1.85135 nd52 (refractive index of secondlens L₃₅₂, with respect to d-line) = 1.54814 nd51 − nd52 = 0.303 (Valuesrelated to conditional expression (4)) νd12 (Abbe number of second lensL₃₁₂, with respect to d-line) = 95.10 (Values related to conditionalexpression (5)) νd13 (Abbe number of third lens L₃₁₃, with respect tod-line) = 68.63

FIG. 6 is a diagram of various types of aberration occurring, withrespect to the d-line (λ=587.56 nm), in the zoom lens according to thethird embodiment. S and M shown with respect to astigmatism,respectively indicate aberration at the sagittal image plane and at themeridonal image plane.

FIG. 7 is a cross sectional view (along the optical axis) of the zoomlens according to a fourth embodiment. The zoom lens includessequentially from the object side, a first lens group G₄₁ having apositive refractive power, a second lens group G₄₂ having a negativerefractive power, a third lens group G₄₃ having a positive refractivepower, a fourth lens group G₄₄ having a positive refractive power, and afifth lens group G₄₅ having a negative refractive power.

The aperture stop STP prescribing a given aperture is disposed betweenthe second lens group G₄₂ and the third lens group G₄₃. The cover glassCG is disposed between the fifth lens group G₄₅ and the imaging planeIMG. The cover glass CG is disposed as necessary and may be omittedaccordingly. At the image plane IMG, the light receiving surface of asolid state image sensor, such as a CCD and CMOS, is disposed.

The first lens group G₄₁ includes sequentially from the object side, anegative first lens L₄₁₁, a positive second lens L₄₁₂, a positive thirdlens L₄₁₃, and a positive fourth lens L₄₁₄. The first lens L₄₁₁ and thesecond lens L₄₁₂ are cemented.

The second lens group G₄₂ includes sequentially from the object side, anegative first lens L₄₂₁, a negative second lens L₄₂₂, a positive thirdlens L₄₂₃, and a negative fourth lens L₄₂₄. The first lens L₄₂₁ is ameniscus lens having a convex surface on the object side and bothsurfaces of the first lens L₄₂₁ are aspheric. The third lens L₄₂₃ andthe fourth lens L₄₂₄ are cemented.

The third lens group G₄₃ includes sequentially from the object side, apositive first lens L₄₃₁ and a negative second lens L₄₃₂. Both surfacesof the first lens L₄₃₁ are aspheric. The second lens L₄₃₂ is a meniscuslens having a convex surface on the object side.

The fourth lens group G₄₄ includes sequentially from the object side, apositive first lens L₄₄₁ and a negative second lens L₄₄₂. The surface onthe object side of the first lens L₄₄₁ is aspheric. The first lens L₄₄₁and the second lens L₄₄₂ are cemented.

The fifth lens group G₄₅ includes sequentially from the object side, anegative first lens L₄₅₁ and a positive second lens L₄₅₂. Both surfacesof the first lens L₄₅₁ are aspheric.

The second lens group G₄₂ is moved along the optical axis from theobject side toward the imaging plane IMG side, whereby the zoom lenszooms from the wide angle edge to the telephoto edge. The fourth lensgroup G₄₄ is moved along the optical axis, whereby the zoom lenscorrects image plane variations accompanying zooming and performsfocusing. The first lens group G₄₁, the third lens group G₄₃, and thefifth lens group G₄₅ remain stationary.

Here, various values related to the zoom lens according to the fourthembodiment are given.

Focal length of entire lens system = 4.3 (wide angle edge) to 24.0(intermediate focal position) to 129.0 (Ft: telephoto edge) F number =1.6 (wide angle edge) to 3.8 (intermediate focal position) to 4.9(telephoto edge) Half-angle (ω) = 38.01 (wide angle edge) to 7.10(intermediate focal position) to 1.32 (telephoto edge) (Lens Data) r₁ =144.159 d₁ = 1.00 nd₁ = 1.84666 νd₁ = 23.78 r₂ = 38.899 d₂ = 5.80 nd₂ =1.49700 νd₂ = 81.60 r₃ = −273.198 d₃ = 0.10 r₄ = 52.998 d₄ = 3.31 nd₃ =1.59282 νd₃ = 68.63 r₅ = 378.875 d₅ = 0.10 r₆ = 31.113 d₆ = 3.57 nd₄ =1.83481 νd₄ = 42.72 r₇ = 92.838 d₇ = D(7) (variable) r₈ = 76.499(aspheric) d₈ = 0.70 nd₅ = 1.85135 νd₅ = 40.10 r₉ = 6.041 (aspheric) d₉= 3.30 r₁₀ = −12.953 d₁₀ = 0.50 nd₆ = 1.88300 νd₆ = 40.80 r₁₁ = 71.416d₁₁ = 0.10 r₁₂ = 18.115 d₁₂ = 1.99 nd₇ = 1.94594 νd₇ = 17.98 r₁₃ =−26.555 d₁₃ = 0.50 nd₈ = 1.88300 νd₈ = 40.80 r₁₄ = 95.601 d₁₄ = D(14)(variable) r₁₅ = ∞ (aperture stop) d₁₅ = 0.50 r₁₆ = 11.217 (aspheric)d₁₆ = 4.40 nd₉ = 1.61881 νd₉ = 63.85 r₁₇ = −25.000 (aspheric) d₁₇ = 0.96r₁₈ = 22.880 d₁₈ = 0.60 nd₁₀ = 2.001 νd₁₀ = 29.13 r₁₉ = 10.741 d₁₉ =D(19) (variable) r₂₀ = 11.970 (aspheric) d₂₀ = 4.20 nd₁₁ = 1.4971 νd₁₁ =81.56 r₂₁ = −9.300 d₂₁ = 0.60 nd₁₂ = 1.90366 νd₁₂ = 31.32 r₂₂ = −13.445d₂₂ = D(22) (variable) r₂₃ = 41.730 (aspheric) d₂₃ = 0.50 nd₁₃ = 1.85135νd₁₃ = 40.10 r₂₄ = 6.749 (aspheric) d₂₄ = 0.49 r₂₅ = 17.244 d₂₅ = 2.13nd₁₄ = 1.56732 νd₁₄ = 42.80 r₂₆ = −10.867 d₂₆ = 1.00 r₂₇ = ∞ d₂₇ = 2.00nd₁₅ = 1.51633 νd₁₅ = 64.14 r₂₈ = ∞ d₂₈ = 3.50 r₂₉ = ∞ (imaging plane)Constants of the cone (k) and aspheric coefficients (A, B, C, D) (eighthplane) k = 0, A = −2.65503 × 10⁻⁴, B = 1.28344 × 10⁻⁵, C = −3.59136 ×10⁻⁷, D = 3.83400 × 10⁻⁹ (ninth plane) k = 0.3239, A = −5.45623 × 10⁻⁴,B = −7.61065 × 10⁻⁶, C = 7.83466 × 10⁻⁷, D = −5.46724 × 10⁻⁸ (sixteenthplane) k = −0.1982, A = −5.20814 × 10⁻⁵, B = −1.30668 × 10⁻⁶, C =1.67967 × 10⁻⁸, D = −1.13589 × 10⁻¹⁰ (seventeenth plane) k = −6.0844, A= 7.14760 × 10⁻⁵, B = −1.84345 × 10⁻⁶, C = 2. 96044 × 10⁻⁸, D = −1.85685× 10⁻¹⁰ (twentieth plane) k = −0.2645, A = −5.95055 × 10⁻⁵, B = −1.16644× 10⁻⁶, C = 7.95351 × 10⁻⁹, D = 3.24336 × 10⁻¹⁰ (twenty-third plane) k =0, A = −3.71965 × 10⁻⁴, B = −2.63704 × 10⁻⁵, C = 2.26085 × 10⁻⁶, D =−6.30326 × 10⁻⁸ (twenty-fourth plane) k = 0.0775, A = −2.57754 × 10⁻⁴, B= −3.45586 × 10⁻⁵, C = 9.86053 × 10⁻⁷, D = 3.54356 × 10⁻¹⁰ (Zoom Data)wide angle intermediate telephoto edge focal position edge D(7) 0.89719.167 27.163 D(14) 28.094 9.824 1.828 D(19) 10.148 4.496 14.112 D(22)4.564 10.216 0.600 (Values related to conditional expression (1)) f51(focal length of first lens L₄₅₁) = −9.520 Y (image height) = 3.4|f51|/Y = 2.8 (Values related to conditional expression (2)) F5 (focallength of fifth lens group G₄₅) = −90.419 |F5/Ft| = 0.701 (Valuesrelated to conditional expression (3)) nd51 (refractive index of firstlens L₄₅₁, with respect to d-line) = 1.85135 nd52 (refractive index ofsecond lens L₄₅₂, with respect to d-line) = 1.56732 nd51 − nd52 = 0.284(Values related to conditional expression (4)) νd12 (Abbe number ofsecond lens L₄₁₂, with respect to d-line) = 81.60 (Values related toconditional expression (5)) νd13 (Abbe number of third lens L₄₁₃, withrespect to d-line) = 68.63

FIG. 8 is a diagram of various types of aberration occurring, withrespect to the d-line (λ=587.56 nm), in the zoom lens according to thefourth embodiment. S and M shown with respect to astigmatism,respectively indicate aberration at the sagittal image plane and at themeridonal image plane.

Among the values for each of the embodiments, r₁, r₂, . . . indicateradii of curvature for each lens, aperture stop surface, etc.; d₁, d₂, .. . indicate the thickness of the lenses, aperture stop, etc. or thedistance between surfaces thereof; nd₁, nd₂, . . . indicate therefraction index of each lens with respect to the d-line (λ=587.56 nm);and υd₁, υd₂, . . . indicate the Abbe number of each lens with respectto the d-line (λ=587.56 nm). Lengths are indicated in units of [mm] andangles are indicated in [degrees].

Each of the aspheric surfaces above is expressed by the followingequation, where Z is the depth of the aspheric surface, R is theparaxial radius of curvature, h is the height from the optical axis, andthe traveling direction of light is positive.

$\begin{matrix}{Z = {\frac{y^{2}}{R\left\{ {1 + {1\sqrt{1 - {\left( {1 + k} \right){y/R^{2}}}}}} \right\}^{2}} + {Ay}^{4} + {By}^{6} + {Cy}^{8} + {Dy}^{10}}} & \lbrack 1\rbrack\end{matrix}$

Further, k is the constant of the cone, and A, B, C, and D are thefourth, the sixth, the eighth, and the tenth order asphericcoefficients, respectively.

As described, the zoom lens of each of the embodiments includes lenseshaving suitable aspheric surfaces and cemented lenses and by satisfyingthe conditional expressions above, achieves a large aperture ratio of anF number on the order of 1.6, and can implement an imaging lens that iscompact and has high optical performance as well as a high zoom ratio(on the order of 30×) and that is suitable for compact imagingapparatuses equipped with a full high vision solid state image sensors.

As described, the zoom lens according to the present invention is usefulfor compact imaging apparatuses equipped with a solid state imagesensor, such as a digital still camera and a digital video camera. Inparticular, the zoom lens is optimal for a surveillance camera equippedwith a full high vision solid state image sensor.

According to the present invention, resolution of the optical system canbe further improved.

According to the present invention, chromatic aberration particularly atthe telephoto edge can be favorably corrected.

According to the present invention, spherical aberration and coma overthe entire zoom range can be favorably corrected.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

The present document incorporates by reference the entire contents ofJapanese priority document, 2012-042554 filed in Japan on Feb. 28, 2012.

What is claimed is:
 1. A zoom lens comprises sequentially from an objectside, a first lens group having a positive refractive power, a secondlens group having a negative refractive power, a third lens group havinga positive refractive power, a fourth lens group having a positiverefractive power, and a fifth lens group having a negative refractivepower, wherein the first lens group, the third lens group, and the fifthlens group remain stationary, the second lens group is moved along anoptical axis, from the object side toward an image side, whereby zoomingfrom a wide angle edge to a telephoto edge is performed, the fourth lensgroup is moved along the optical axis, whereby image plane variationaccompanying zooming is corrected and focusing is performed, the fifthlens group includes sequentially from the object side, a negative firstlens having at least one aspheric surface and a positive second lens,and the zoom lens satisfies: a conditional expression (1) 1.5<|f51|/Y<3,and a conditional expression (2) 0.2<|F5/Ft|<0.8, where, f51 is a focallength of the first lens in the fifth lens group, Y is an image heightfor the entire optical system, F5 is a focal length of the fifth lensgroup, and Ft is a focal length of the entire optical system at thetelephoto edge.
 2. The zoom lens according to claim 1, wherein the fifthlens group includes the first lens and the second lens, and the zoomlens satisfies a conditional expression (3) nd51−nd52>0.2, where, nd51is a refractive index (with respect to the d-line) of the first lens inthe fifth lens group and nd52 is a refractive index (with respect to thed-line) of the second lens in the fifth lens group.
 3. The zoom lensaccording claim 1, wherein the first lens group includes sequentiallyfrom the object side, a negative first lens, a positive second lens, apositive third lens, and a positive fourth lens, the first lens and thesecond lens in the first lens group are cemented, and the zoom lenssatisfies: a conditional expression (4) υd12>75, and a conditionalexpression (5) υd13>63, where, υd12 is an Abbe number (with respect tod-line) of the second lens in the first lens group and υd13 is an Abbenumber (with respect to the d-line) of the third lens in the first lensgroup.
 4. The zoom lens according to claim 1, wherein the third lensgroup includes sequentially from the object side, a positive first lenshaving at least one aspheric surface and a negative second lens that isa meniscus lens having a convex surface on the object side.
 5. The zoomlens according to claim 2, wherein the third lens group includessequentially from the object side, a positive first lens having at leastone aspheric surface and a negative second lens that is a meniscus lenshaving a convex surface on the object side.